Capacitive touch screens can be categorized as self-inductive capacitive touch screens and mutual inductive capacitive touch screens according to their detection modes for a touch signal. A mutual inductive capacitive touch screen comprises a plurality of drive lines and a plurality of sense lines intersecting orthogonally with the drive lines. Mutual inductive capacitances are formed between the plurality of drive lines and the plurality of sense lines, where the capacitances at the locations where the plurality of drive lines and the plurality of sense lines overlap are unchangeable by an outside touching object, and the mutual inductive capacitances resulting from fringe electric fields generated at the locations where no electrodes overlap are influenced by an outside touching object.
FIG. 1 is an electrode structure of a typical mutual inductive capacitive touch screen in the prior art. A space between two diamond-shaped electrodes determines the capacitance of a mutual inductive capacitance C and also the maximal amplitude of a signal. This is because the mutual inductive capacitance varies when a finger is pressed against the surface of the touch screen while a press trace of the a finger covers a part of area or all area of a gap region of the mutual inductive capacitance, and variation of signal output by the plurality of sense lines is proportionate to variation of mutual inductive capacitance.
FIG. 2 illustrates a shape of press trace of a finger, movement directions of the finger and shape of a gap region of a mutual inductive capacitance, where there are two directions D1 and D2 in which the finger may move. When the finger moves in different direction respectively denoted by D1 or D2, variation of the mutual inductive capacitance C (see FIG. 1) exhibit different variation curves. As illustrated in FIG. 3, a variation curve L1 and a variation curve L2 can be calculated from the mutual inductive capacitance C with the electrode structure illustrated in FIG. 1 and the respective directions D1 and D2 in which the finger moves as illustrated in FIG. 2. The variation curve L1 and the variation curve L2 correspond respectively to the movement directions D1 and D2 , and K represents time or distance of the finger movement. We notice that firstly the electrode structure of a touch screen as illustrated in FIG. 1 results in an anisotropic detection characteristic and secondly the variation curves of the mutual inductive capacitance are unsmooth. This will cause noise in temporal or spatial differentiation of the output signal, thus degrading a resolution of the touch signal at high spatial frequencies and temporal frequencies.